Electrical contact heater



Oct. 29, .1946. A. A. REISER ELECTRICAL CONTACT HEATER Filed Sept. 26, 1942 3 Sheets-Sheet} AT TORNEYS Oct. 29, 1946. RE|$ER ELECTRICAL CONTACT HEATER s Sheets-Sheet 2 Filed Sept. 26, 1942 9004 WOW ATTORNEYS s Sheets-Sheet 5 W v O A. A. REISER ELECTRICAL CONTACT HEATER Filed Sept. 26, 1942 Oct. 29, 1946.

INVENTOR.

TTORNEQ Patented Oct. 29, 1946 UNITED STATES PATENT I OFFICE 2,410,362 ELECTRICAL CONTACT HEATER Alfred A. Reiser, Buffalo,- N. Y.', a'ssi'gnor, by mesne assignments, to H; & -A. Manufacturing (30.; Binghamton, N. Y., a partnership composed of Maurice Harowitch, Clarence H. Ackley, and Harold Horowitz I 7 Application September 26, 1942, Serial No. 459,793 14 Claims. (01. 219-19) This invention relates to an electrical contact heater and more particularly to a contact heater for maintaining a minimum temperature of the mechanism of machine guns or cannon, particularly when used in aircraft, to prevent the mechanism of the gun or cannon from jamming under the low temperatures encountered at higher levels. The invention is no't, however-, limited to this particular use and can be embodied in any type of electrical contact heater where the features of the invention can be advantageously employed.

one of the difiiculties which has been encountered in aerial combat work is that at the low temperatures encountered at higher atmospheric levels the mechanism of the machine guns and cannon is' liable to freeze and hence render the gun or cannon inoperative. Once the gun fires its own heat is sufiicient to maintain it at an operating temperature and the difiiculty is encountered in maintaining the temperature of the gu mechanism prior to the first burst of fire. To solve this problem it has been the practice to use hot air or the like to prevent the temperature of the gun mechanism from dropping below, for example, F. Such anheating devices are, however, bulky and obstructive to the ready operation of the gun or cannon.

It is accordingly the principal object of the present invention to supply an electrical contact heat-er which will maintain the mechanism of a machine gun at a minimum temperature which prevents the parts from jamming and insures the initial free operation of the gun. i h v Another object of the invention is to provide such an' electrical contact heater which will operate within the maximum wattage available for this purpose, the electrical power plant of a combat plane having limitations in the amount of current which can be withdrawn for gun heating purposes. I

It is another object of the present invention to provide such a contact heater which insures the'niakimum amount of heat being transferred to the gun mechanism which must be kept at a minimum temperature and which avoids the dissip'ation of heat tocthe'r parts of the gun or to the surrounding atmosphere.

Afibthr Object of the invention is to provide such an" electrical contact heater the efficiency or which will not be disturbed' by the recoil of the gun or cannon on it is mounted.

Anotheraim is to provide such an electrical contact heater which does not interfere with'the 2 free operation of the gun or the discharge of shells therefrom.

Another object of the invention is to provide such an electrical contact heater which can be easily attached to the mechanism to be heated and readily removed therefrom.

Another object is to provide such an electrical contact heater which is connected with the cover of the chamber to be heated in such manner that the cover can readily be lifted, together with the contact heater, and readily replace the heater thereby not interfering with the ready inspection or adjustment of the mechanism contained within the chamber to be heated.

Another object of the invention is to provide such a heater in which the heating elements are se'ctionalized so that if one is rendered inoperative the balance will continue to function.

Another object is to provide such a contact heater which is free from any danger of igniting any surrounding gasc-lene fumes or the like.

Another object of the invention is to provide such a contact heater which is simple, inexpensi've and light in construction; is low in cost of production and which will stand up under conditions of severe and constant use Without getting out of order or requiring repairs.

In the accompanying drawings:

Fig. 1 is a perspective view of an electrical contact heater embodying my invention.

2 is an enlarged side elevation thereof and showing the same applied to a machine gun which is indicated by broken lines.

Fig. 3 is a top plan view thereof.

Fig. 4 is a vertical longitudinal section, taken on line 4 -4,-Fig. 3.

Fig. 5 is a vertical transverse section, on'line 5--5,'Fig. 2.

Fig. 6 is a vertical longitudinal section, on line 6-6, Fig. 5.

Fig. 7 is a vertical transverse section taken on line 1- 1, Fig. 6.

8 is' a fragmentary vertical section, taken on line 88,Fig. 2. v v w h Fig. 9 is a diagrammatic representation of the wiring system of the con'tact heater.

The electrical contact heater is shown as mounted on a machinegun A having side walls B and a removable cover C which is provided withflanges D fitting over the side walls B and enclosing a chamber This chamber E contains the operating mechanism of the machine gun (not shown) which it is desirable to maintain at a minimumtemperature of, say, O" F.'t'o prevent the oil-of these parts from congealing and taken taken thereby render the gun inoperative. One wall B of the machine gun is shown as having an exteriorly projecting bolt head F which interferes with the planar form of the side walls B of the gun and around which the heater embodying the present invention is fitted, as hereinafter described.

The contact heater embodying the present invention is shown as including a casing I made of sheet steel to have the necessary strength and resilience and having a rectangular top II and sides I2 and I3 which are bent downwardly from the longitudinal side edges of the top II. To flt the particular machine gun shown, the side wall I2 is recessed at one end, as indicated at I4, to leave a stepped flange I5 projecting downwardly from the corresponding side edge of the top II at that end of the casing, and similarly the Opposite side wall I3 is recessed at the corresponding end, as indicated at IE, to leave a flange I8 projecting downwardly from the opposite side edge of the top II. Further, to fit the particular machine gun shown, the side wall I3 is centrally recessed, as indicated at l9, so that this side wall can be fitted downwardly around the head of the bolt F which projects from the corresponding side wall B of the gun as previously described.

One end of the top II is bent downwardly to provide 9. depending end flange and the opposite end of this top is bent downwardly to provide an opposite end flange 2|. The opposite ends of the side wall I2 are bent inwardly to provide inwardly projecting end flanges 22 and 23 and similarly the opposite ends of the side wall I3 are bent inwardly to provide inwardly projecting end flanges 24 and 25. The side wall l3 at the generally vertical edges of the recess I9 is bent to provide inwardly projecting flanges 28 and 29. The lower horizontal edges of the side walls I2 and I3 are bent to provide downwardly and inwardly inclined flanges which fit against the lower edges of the corresponding vertical flanges 22-29 and the lower extremities of these inclined lower flanges are bent upwardly to provide lips 3|.

six

The flanges 22, 23 and 30 of the side wall I2 form a pocket receiving a rigid heat pad 350.. The flanges 24, 28 and 30 of the sid wall I3 form a pocket for the reception of a rigid heating pad 35?), and the flanges 25, 29 and 30 form a pocket for the reception of a rigid heating pad 35c. As these pads 35a, 35b and 350 are identical, except as to size and shape, the following description of one applies to all three:

Each of these rigid heating pads is shown as housed within a shell 36 made of sheet copper or other metal havin a high rate of heat transfer and as having one broad vertical wall 37 which flts flat against the corresponding side wall 13 of the machine gun and from the opposite generally vertical edges of which flanges 38 project outwardly. Along its upper horizontal edge the wall 31 of each of the pads is flanged, as indicated at 39, this flange extending upwardly and outwardly parallel with the flange 30 along the lower edge of the corresponding side wall of the casing I0, and along its lower edge the wall 31 of each of the pads is flanged as indicated at 40, this flange projecting upwardly and outwardly parallel with the opposite flange 39. Th broad vertical wall 31 is preferably provided with its marginal flanges 3840 by stamping so that each shell 38 is of cup-shaped form and free from holes or soldering.

In the bottom of the cup-shaped shell 36 of each heating pad is arranged a sheet of dielectric material, such as mica, such material also preferably having a relatively high rate of heat transfer. Against the outer face of this sheet 45 is arranged the resistance wiring 4B. This resistance wiring can be of any suitable form to impart the desired heat and is purely diagrammatically shown as a wire extending back and forth along the outer face of the sheet 45. This resistance wiring is shown as being backed by several sheets 48 of non-electrical conducting and low thermal conductive material, such as asbestos. The resistance wiring and the mica and asbestos sheets are then sealed in the cupshaped shell 35 by a layer 49 of a synthetic resin or other hard setting material which will not melt at the temperatures developed by the resistance wiring and which is poured into the cupshaped shell after it has been filled with the mica and asbestos sheets and the resistance wiring and permitted to harden. The rigid heat pads 35a, 35b and 350 are therefore of sealed water-proof construction and the leads 5!) and 5i for the resistance wiring 40 can be brought out in any suitable manner.

The leads 50 and 5| from the resistance wiring of the several rigid heating pads 35a, 35b and 350 extend upwardly from these heating pads and are arranged along the underside of the top I I of the steel shell I0, as best shown in Figs. 3-7. As best illustrated in Figs. 4 and 9, the leads 5!! are commoned and similarly the leads 5i are interconnected, this being preferably accomplished by bars secured to the underside of a block 5?. which is in turn secured to the underside of the top II of the steel casing II], as best shown in Figs. 3 and 4. These bars are respectively connected to the opposite sides of a source of electrical energy 53 which is conventionally illustrated as being a battery but which may be the generator of the airplane. As best shown in Figs. 1 and 2, the lines connecting the heater with the source of electrical energy 53 are brought out from the side of the casing III in the form of a cable 54. It will be noted that the several sets of resistance wiring 46 are connected in parallel so that in the event that one should be broken in combat, the remaining heating elements will function to heat the gun.

An important feature of the invention resides in the manner of mounting the rigid heating pads 35a, 35b and 350 in place, it being highly important that the broad walls 31 of these heating pads fit flat against the side walls B of the gun casing to insure a high rate of heat transfer and it also being important to leave an air space between these heating pads and the casing I0 and to otherwise reduce, so far as possible, all heat transfer from the heating pads to the steel case II). It will be appreciated that the loss of heat to the surrounding air reduces the heat transmitted to th mechanism within the chamber E and hence reduces the efliciency of the heater as a whole. To this end, as best illustrated in Figs. 2 and 8, the lower inclined flange 40 of each of the heating pads 35a, 35b and 350 carries a pair of spaced pins 55 which can be secured thereto in any suitable manner and which project outwardly into an opening 55 provided in the corresponding lower inclined flange 30 of the steel shell ID. A spacing washer 51 can be provided around each pin 55 and is shown as soldered to the inner face of the inclined flange 30 of the steel shell. The ins 50 and holes 56 are so located as to leave an air space 58 between each heating pad and the correspond ing side leg or wall I! or l3 f the steel case l0.

At its upper end each of the heating pads 35a, 35b and 350 is held against a bracket 60 As best shown in Figs. 6 and '7, each of these brackets comprises a vertical upper leg 6! which is fitted against the inside of the corresponding side wall l2 or [3 of the steel casing and secured thereto at its upper end by a rivet 62 and at its lower end by a bolt 63 having a nut 64 which bears against the bracket 60. This bracket 6'0 is also formed to provide a lower leg 65 which projects downwardly and inwardly parallel with the bottom flanges 30 0f the side walls ['2 0r I 3 of the steel casing and hence parallel with the upper and lower flanges 39 and 40 of the corresponding heating pad. The upper flange 39 of this corresponding heating pad fits against the under side of this inclined leg 65 of the bracket 60 andis held thereagainst by a leaf spring 66 which is secured to the inside of the corresponding side wall or leg l2, l3 of the steel shell, as best shown in Figs. -7 and presses inwardly against the upper edge of the corresponding heating pad. Each of the brackets is also formed at its lower end to provide an inwardly projecting horizontal lip 68 which is arranged to engage the underside of the corresponding edge of the cover C of the machine gun as best shown in Fig. 7.

It will be seen that by this arrangement the air space 5 8 is left between each heating pad and the adjacent portion of the steel shell I0 and further that the connection between each heating pad and this shell is such that there is a very small heat transfer from the heating pad to the steel shell. It will further be seen that each heating pad is flexibly secured to the steel shell and is yieldingly urged inwardly by the leaf spring 66 and that this flexible connection is such as to permit bodily movement of the heating pad inwardly and outwardly and also so as to permit the heating pad to tilt about a vertical, horizontal or inclined axis. Therefore, when the heater is applied to the machine gun, each heating pad is I free to adapt itself and come into flat planar contact with the side walls B of the machine gun, this planar fitting of each heating pad against the machine gun insuring proper heat transfer. It will further be seen that the brackets 60 which secure the heating pads in place also serve to hold the heater casing in place, inasmuch as these brackets are provided with the lips 68 which fit under the cover C of the machine gun.

This cover Cof the machine gun is surrounded by a layer 10 of hair felt or other suitableinsdlating material which can be secured to the steel casing in any suitable manner. As shown, that is accomplished by a strip H of any suitable fibrous material which fits against the top of the cover C of the machine gun and is provided at its opposite end with upturned flanges 12 each of which is secured to the inner side of the corresponding end flange 20, 2| of the top H .of the steel casing ID by the ends of a wire clip 13, as

best shown in Figs. 3 and 4. The strip H of fibrousmaterial is preferably urged into firm engagement with the cover C of the machine gun by a pair of helical compression springs 15-, as best shown in Figs. 3 and 4. This strip ll of fibrous material can also be slotted or otherwise perforated, as indicated at 16, Fig. 4, to receive any projection 11 on the upper side of the cover C- of the machine gun.

In applying the unit to the machine gun A the legs or sides I2, l3*of the steelshel'l can be spread apart as indicated by the dot-dash lines in Fig. 7. This permits the'unit to be placed over the cover C of the machine gun, the unit thereby assuming the dot-dash line position shown in Fig. 4. The unit is then pressed downwardly into the full line position shown in Fig. 4,. the strip H of fibrous material being thereby pressed flat against the cover 0 of the machine gun against the resistance of the pair' of helical compression springs 15. T-he side walls 'or legs [2, i3 of'the steel case are then pressed together so that the lips 68 of the brackets 60 engage under the side edges of the cover C of the machine gun. In

. so bringing in these side legs or walls of the steel casing the heating pads a, 35b and 350 adapt themselves to the side walls B of the machine gun and fit against them in direct planar relation.

This position of the unit, illustrated by full lines in the drawings, is maintained by a pair of U-shaped metal yokes 80 the central cross .part 8| of which is journaled in a pair of ears'82 provided on the top H of the steel casing 10. Each of these yokes 80 is of heavy relatively rigid construction and is provided with a pair of depend i'ng arms 83 which embrace the opposite side walls or legs [2, I3 of the steel casing. Each of the arms 83 of these rigid yokes fit into a notched lug 84 which is suitably secured to the corresponding side wall ['2 or l3 of the steel casing H]. The arms 83 of these yokes 80 are not of themselves springy but press against the side walls or legs l2, l3 of the steel casing '30, these side walls or legs of themselves being springy and also acting through the leaf springs 66 against the rigid heating pads 35a, 35b and 350 to hold these pads firmly in true planar engagement with the sides B of the gun.

In installing the contact heater embodying the invention upon a machine gun, the yokes as are first swung so that their legs occupy an upright position, this permitting the side walls or legs I2, [3 of the steel shell 16 to spring to the dotdash lines shown in Fig. 7. The heater is then placed over the'machine gun A and the fiber strip H is pressed downwardly upon the cover C of the machine gun against the resistance of the helical compression spring 15. The sides or legs l2, l3

of the casing are then pressed inwardly so as to.

bring the several heating pads 35a, 35b and 350 into contact with the side walls B of the gun. The legs 83 of the yokes 80 are then swung downwardl-y and engaged with the notched lugs 84,.

In bringing the side legs or walls l3 of the easi'ng together, the lips 68 "of the bracket are brought under the lower edges of the cover 0 so as to lock theheater in position on the machine gun. At the same time, since the mounting of the heating pads 35a, 35b and 350 is such as to permit these pads to turn in any direction, the heating pads are free to adapt themselvesto the side walls B of the gun and to come into true pl'anar'contac't therewith. This insures the maximum heat transfer between the broad flat'walls 31 of these heating pads and the sides B of'thegun and hence insures the maximum heating of the parts (not shown) contained within the chamber E. At the same time, the air space 58. is maintained between each heating pad and the supporting shell IO'of the heater so that the loss of heat to the outside atmosphere is reduced.

From the foregoing it will be seen that the present invention provides a very simple, inexy pensive and effective electric contact heater, par ticularly for maintaining a minimum tempora ture of the operating mechanism of a machine gun; which can readily be installed upon the machine gun or removed therefrom; which does not interfere with the opening of the cover on which it is mounted; which is so constructed as to avoid the danger of igniting any gasolene fumes; which insures the maximum amount of heat being transferred to the part of the machine gun to be heated with a minimum dissipation of heat; and which accomplishes the other objects of the invention as hereinbefore stated.

I claim as my invention:

1. An electrical contact heater of the character described, comprising a U-shaped casing of resilient material adapted to embrace the part to be heated, a rigid electrical heating pad arranged inside of said casing and loosely secured to one leg thereof to permit it to adapt itself to the exterior surface of the part to be heated, and means yieldingly urging said legs of said casing toward each other to hold said heating pad in firm thermal contact with said surface, comprising a U-shaped yoke having its cross part journaled on the cross part of said U-shaped casing and having rigid legs adapted to engage retaining lugs provided on the exterior of the legs of said U-shaped casing.

2. An electrical contact heater of the character described, comprising a U-shaped sheet metal casing adapted to embrace the part to be heated the extremity of one of the legs of said casing being provided with an inturned flange, a rigid electrical heating pad arranged within said casing and loosely secured at one margin to said inturned flange and in spaced relation to the corresponding leg of said casing to provide a thermal insulating air space between said heating pad and said corresponding leg, means for loosely securing the opposite margin of said heating pad to said corresponding leg to permit said heating pad to adapt itself to the exterior surface of the part to be heated, and means yieldingly urging said corresponding leg of said casing toward said part to be heated and thereby hold said heating pad in firm thermal contact with said surface.

3. An electrical contact heater of the character described, comprising a U-shaped sheet metal casing adapted to embrace the part to be heated the extremity of one of the legs of said casing being provided with an inturned flange, a rigid electrical heating pad arranged within said casing, a pin loosely connecting one margin of said heating pad with said inturned flange and holding said heating pad in spaced relation to the corresponding leg of said casing. to provide a thermal insulating air space between said heating pad and said corresponding leg, means for loosely securing the opposite margin of said heating pad to said corresponding leg to permit said heating pad to adapt itself to the exterior surface of the part to be heated, and means yieldingly urging said corresponding leg of said casing toward said part to be heated and thereby hold said heating pad in firm thermal contact with said surface.

4. An electrical contact heater of the character described, comprising a U-shaped sheet metal casing adapted to embrace the part to be heated the extremity of one of the legs of said cal,- ing being provided with an inturned flange, a rigid electrical heating pad arranged within said casing and loosely secured at one margin to said inturned flange and in spaced relation to the corresponding leg of said casing to provide a thermal insulating air space between said heating pad and said corresponding leg, a bracket Secured to the inside of said corresponding leg adjacent the opposite margin of said pad, means loosely securing said opposite margin of said heating paid to said bracket to permit said heating pad to adapt itself to the exterior surface of the part to be heated, and means yieldingly urging said corresponding leg of said casing toward said part to be heated and thereby hold said heating pad in firm thermal contact with said surface.

5. An electrical contact heater of the character described, comprising a U-shaped sheet metal casing adapted to embrace the part to be heated, the extremities of the downwardly projecting legs of which are each provided with an inwardly and downwardly projecting flange, a heating pad arranged within said casing adjacent each leg thereof and each comprising a cup-shaped metal holder and electrical resistance wiring in said holder insulated therefrom, the upper and lower parts of the rim of each cup-shaped holder being inclined generally parallel with the flange of the corresponding leg, means loosely securing the lower inclined part of the rim of each holder to the flange of the corresponding leg and holding the heating pads in spaced relation to the legs of said casing to provide thermal insulating air spaces between said heating pads and legs, a bracket secured to each leg of said casing adjacent the upper part of the rim of each heating pad and having an inclined lower end adapted to fit against the inclined upper part of the rim of the corresponding heating pad, spring means between each heating pad and the corresponding leg of said casing and yieldingly holding each heating pad in engagement with the corresponding bracket, and means yieldingly urging said legs of said casing toward each other to hold said heating pads in firm thermal contact with the surface to be heated.

6. An electrical contact heater for heating a part having a cover provided with downturned flanges embracing said part, comprising a U- shaped sheet metal casing having its cross part arranged over said cover and having depending side legs embracing the sides of the part to be heated, a rigid electrical heating pad loosely secured at its lower end to the lower extremity of each of the legs of said casing and spaced from the correspondingleg of said casing to provide a thermal insulating air space between each heating pad and the corresponding leg of said casing, a bracket secured to the inside of each leg of said casing adjacent the upper end of the corresponding heating pad, means loosely securing the upper end of each heating pad to said bracket to adapt itself to the exterior sur-- face of the part to be heated, the end of each of said brackets being formed to fit under the said downturned flanges of said cover, and means yieldingly urging the legs of said casing toward each other and thereby hold said heating pad in firm thermal contact with said surface.

7. An electrical contact heater for heating a part having a cover provided with downturned flanges embracing said part, comprising a U- shaped sheet metal casing having its cross part arranged over said cover and having depending side legs embracing the sides of the part to be heated, a rigid electrical heating pad loosely secured at its lower end to the lower extremity of each of the legs of said casing and spaced from the corresponding leg of said casing to provide a thermal; insulating ai space between each heating pad and the corresponding leg of said casing, a bracket secured to the inside of each leg of said casing adjacent the upper end ofthe corresponding heating pad, means loosely securing the upper end of each heating pad to said bracket to adapt itself to the exterior surface of the partto be heated, the end of each of said brackets being formed to fit under the said downturned flanges of said cover, means yieldingly urging the legs of said casing toward each other and thereby hold said heating pad n firm thermal contact with said surface, and spring means interposed between said cover and said cross part of said casing and yieldingly urging said casing upwardly to hold said brackets firmly in engagement with the under side of the downturned flanges of said cover.

8. An electrical contact heater for heating a part having a cover provided with downturned flanges embracing said part, comprising a U- shaped sheet metal casing having its cross part arranged over said cover and having depending Side legs embracing the sides of the part to be heated, a rigid electrical heating pad loosely secured at its lower end to the lower extremity of each of the legs of said casing and spaced from the corresponding leg of said casing to provide a thermal insulating air space between each heating pad and the corresponding leg of said casing, a bracket secured to the inside of each leg of said casing adjacent the upper end of the corresponding heating pad, means loosely securing the upper end of each heating pad to said bracket to adapt itself to the exterior surfaceof the part to be heated, the end of each of said brackets being formed to fit under the said downturned flanges of said cover, means yieldingly urging the legs of said casing toward each other and thereby hold said heating pad in firm thermal contact with said surface, a flexible strip arranged under said cross part of said casing and secured at its ends to the opposite ends of said cross part, and spring means interposed between said flexible strip and said cross part of said casing and yieldingly urging said casing upwardly to hold said brackets firmly in engagement with the under sides of the downturned flanges of said cover.

9. An electrical contact heater for heating a part having a cover provided with downturned flanges embracing said part, comprising a U- shaped sheet metal casing having its cross part arranged over said cover and having depending side legs embracing the sides of the part to be heated, a rigid electrical heating pad loosely secured at its lower end to the lower extremity of each of the legs of said casing and spaced from the corresponding leg of said casing to provide a thermal insulating air space between each heating pad and the corresponding leg of said casing, a bracket secured to the inside of each leg of said casing adjacent the upper end of the corresponding heating pad, means loosely securing the upper end of each heating pad to said bracket to adapt itself to the exterior surface of the part to be heated, the end of each of said brackets being formed to fit under the said downturned flanges of said cover, means yieldingly urging the legs of said casing toward each other and thereby hold said heating pad in firm thermal contact with said surface, a flexible strip arranged under said cross part of said casing and secured at its ends to the opposite ends of said cross part, a packing of insulating material interposed between said flexible strip and said cross part of said casing, and spring means interposed between said flexibl strip and said cross part of said casing and yieldingly urging said casing upwardly to hold said brackets firmly ineng-agem nt with-the under sides of the downturned flanges of said; cover.

10. electrical contact heater of the -character described, comprising a U-shaped metal casing adapted to embrace the part to be heated and provided with inturned flanges alon the edges of its side legs and cross part thereby to provide internal pockets in its side legs and cross part, an electrical heating pad loosely mounted in each of the pockets of said side legs thereby to permit said heating pads to adapt themselves to the surface of said part to be heated and said pads being held in spaced relation to said side legs to provide thermal insulating air spaces between said heating pads and side legs, insulating material arranged in the pocket of said cross part of said casing and engaging the corresponding surface of the part to be heated, and means for yieldingly urging the legs of said casing toward each other to hold said heating pads in firm thermal contact with the part to be heated.

11. A heating apparatus comprising in combination a plurality of heating pads arranged in thermal contact with two sides of the part to be heated, a flexible channel-shaped casing embracing said two sides of the part to be heated and said heatin pads in spaced relation thereto and bodily movable with respect thereto, spring means interposed between each of said heating pads and the adjacent part of said casing, and a rigid U-shaped holder embracing said casing and engaging the exterior thereof in compressive relation thereto and in position to transfer the resultant of the forces of said spring means on one of said sides of said part to be heated to said spring means on the other of said sides of said part to be heated.

12. A heating apparatus comprising in combination a plurality of heating pads arranged in thermal contact with two sides of the part to be heated, a flexible channel-shaped casing embracing said two sides of the part to be heated and said heating pads in spaced relation thereto and bodily movable with respect thereto, spring means interposed between each of said heating pads and the adjacent part of said casing, and a rigid U-shaped yoke secured to and embracing said casing and engaging the exterior thereof in compressive relation thereto and in position to transfer the resultant of the forces of said spring means on one of said sides of said part to be heated to said spring means on the other of said sides of said part to be heated.

13. An electrical contact heater of the character described, comprising a casing of resilient material havin legs adapted to embrace the part to be heated, a rigid electrical heating pad arranged inside of said casing and loosely secured to one leg thereof to permit it to adapt itself to the exterior surfaces of the part to be heated, and means yieldingly urging said legs of said casing toward each other to hold said heating pad in firm thermal contact with said surface, comprising a rigid yoke secured to said casing and having rigid legs embracing said casing and adapted to engage retaining lugs provided on the exterior of the legs of said U-shaped casing.

14. An electrical contact heater of the character described, comprising a casing of resilient 11 material having legs adapted to embrace the part to be heated, the extremity of one of the legs of said casing being provided with an inturned flange, a rigid electrical heating pad arranged within said casing and loosely secured at one side to said inturned flange and in spaced relation to the corresponding leg of said casing to provide a thermal insulating air space between said heating pad and said corresponding leg,

12 means securing the opposite side of said heating pad to said corresponding leg to permit said heating pad to adapt itself to the exterior surface of the part to be heated, and means yieldingly urging said corresponding leg of said casing toward said part to be heated and thereby hold said heating pad in firm thermal contact with said surface.

ALFRED A. REISER. 

